A coordinated set of studies has been completed through the initial phases of (1) preliminary analyses culminating in formulating a set of tentative insights to serve as a guide to preparing final analyses, (2) restructuring of computer file data bases to facilitate further analysis. Major conclusions from studying mice and rats (Mus musculus and Rattus norvegicus) in designed habitats: (1) Behavioral deviance begins to be significant at twice optimum density and by 8 times optimum density produces zero reproductive success, which is followed by population extinction, but isolation of reproductive-aged pairs permits sufficient behavioral recovery for successful rearing of progeny. (2) Habitats consisting of interconnected compartments, arranged to produce a bilaterally symmetrical communication network, enhance preservation of normality of individual behavior and group structure. (3) Provision of opportunity to develop cooperative behavior can largely offset deleterious consequences arising from increase in density. (4) Layered strategies employed by rats in consummating cooperative behavior suggest an increase in conceptualization capacity proportional to the increase in population size.